Today, systems in wind turbines for controlling and operating the wind turbine are based on hydraulic systems. In particular, a pitch servo system and a brake system of a wind turbine may be based on hydraulic systems and components.
In the nacelle of the wind turbine a hydraulic fluid tank or a reservoir and a pump station is installed for supplying the hydraulic fluid to the hydraulic devices. The hydraulic fluid, e.g. hydraulic oil, is pumped to the installation locations of the hydraulic systems and hydraulic components. In particular, the hydraulic fluid may be pumped outside of the nacelle of the wind turbine, such as to the outer placed pitch servo system in a hub of the wind turbine. The hydraulic device may provide accumulator banks, proportional valves and hydraulic actuators, for instance.
Today, in conventional wind turbines comprising hydraulic systems, the fluid level may be measured in the oil tank by a digital oil level sensor. If a leakage turns up in the hydraulic system, in particular at outside located hydraulic devices with a large distance from to the oil tank, a high amount of oil may leak out from the hydraulic device before the oil level sensor may measure the leakage based on recirculation of the hydraulic fluid. Thus, a leakage alarm may be given lately. In the time period between the beginning of the leakage and the alarm initiation a high amount of oil may be already leaked.